The present invention relates to bearing devices comprising a rotary body and bearing means for supporting the rotary body relative to a fixed portion in a noncontact state.
Magnetic bearing devices of the five-axis control type are already known which comprise a rotary body and bearing means for supporting the rotary body relative to a fixed portion without contacting the body. These magnetic bearing devices generally comprise an axial magnetic bearing, two radial magnetic bearings provided toward one end of the rotary body and operable in directions orthogonal to each other, two radial magnetic bearings arranged toward the other end of the rotary body and operable in directions orthogonal to each other, an axial displacement sensor, and eight radial displacement sensors. Each of the magnetic bearings has two electromagnets.
However, the conventional magnetic bearing device of the type mentioned requires the use of large electromagnets since the rotary body is supported relative to the fixed portion in a noncontact state by the attraction of the electromagnets. Moreover the device has the problem that the need to hold the electromagnets energized always during the rotation of the rotary body results in an increased power consumption and entails a higher cost.
Superconducting bearing devices are considered useful as bearing devices of reduced cost. The present applicant has already proposed a superconducting bearing device which comprises a permanent magnet provided on a rotary body, and a superconductor disposed as opposed to the magnet, the permanent magnet being so mounted on the rotary body that the rotation of the rotary body will not alter the magnetic flux distribution around the axis of rotation of the body, the superconductor permitting the penetration of magnetic flux of the permanent magnet thereinto and being disposed at a position which is spaced apart from the magnet by a distance permitting a predetermined quantity of magnetic flux thereof to penetrate thereinto and which will not permit the rotation of the rotary body to alter the distribution of penetrating magnetic flux (see Japanese Patent Application HEI 2-293256). With this device, the rotary body can be supported relative to a fixed portion in a noncontact state merely by cooling the superconductor.
In the case of the superconducting bearing device, however, the magnet carrying portion of the rotary body has a low characteristic frequency, which gives rise to resonance to cause a radial deflection of the rotary body while the rotary body is still in low-speed rotation after the start of rotation before stabilized rotation is attained. In the case where the rotary body is rotated, for example, by a high frequency electric motor which comprises a rotor attached to the rotary body and a stator disposed around the rotor, the radial deflection, if occurring, permits the rotor to undergo a rotational deflection. This rotational deflection is further aggravated by a magnetic imbalance of the motor, consequently causing the rotor to contact the stator to damage or break the motor.